Build Quality

Overall build quality is very solid. There is no rattle when shaking the mouse. When applying lateral pressure, no creaking or flexing of the shell can be observed. Activating the side buttons by squeezing the sides is impossible. Lastly, no accidental clicks occur when slamming down the mouse. However, I did notice a high-pitched noise ("coil whine") even when the sensor is not tracking, simply as long as RGB lighting is enabled.

Buttons

Main buttons on the X15 are good. Both pre and post-travel are moderate, resulting in a somewhat spongy button response. By comparison, the clicks of the X17 and X20 were much better in this regard. On the flip side, the buttons can be spammed with relative ease. Button stiffness is medium to light. A set of LK optical switches (V2, 70 M) is used.

Right next to the left main buttons are two additional buttons, which work just fine. Two tactile switches are used here.


Side buttons are very good. Both pre and post-travel are mostly low, though their response can be mushy. They are positioned similarly to a dial, leaving a spot in the middle unoccupied. Compared to most other MMO mice, which cram the entire left side with buttons, this design leaves some much needed space for the thumb to rest on, which is particularly useful when it comes to avoiding accidentally hitting a button. From this resting position, eight of the ten buttons are readily accessible, and only the two buttons towards the front require some grip readjustment. Further utility is provided by the shift button on the right side. If enabled, another set of binds is made available upon pressing and holding this button, giving one access to 38 binds in total. Ergonomically, this design is excellent, as the button is stiff enough to prevent it from being actuated accidentally or by the weight of one's finger, yet light enough not to be tiresome when holding it for some time. If needed, this functionality can be disabled with the slider on the bottom of the mouse. A TTC Golden Micro Dustproof (60 M) is used for the shift button. Unfortunately, I wasn't able to get the side buttons out of their encasing, so there's no picture of it.

At the top of the mouse are two buttons for cycling through the set CPI levels and profiles. Their click feel is decent. A pair of seemingly unbranded tactile switches is used for these.

Scroll Wheel

The scroll wheel is good. It is rather noisy when scrolling in either direction, but the individual steps are quite nicely separated, resulting in decent tactility. The scroll wheel also allows for horizontal scrolling (tilting, rather), which is useful for productivity work and play as the software allows for rebinding those directions as buttons. Unfortunately, I wasn't able to identify the encoder. Actuating the middle (scroll wheel) click requires medium force. Three seemingly unbranded tactile switches are used here.

Coating

The X15 has a smooth matte surface almost all over. It doesn't attract fingerprints, dirt, or the likes too much, and is easy to clean, but some oil marks can be difficult to get off. All in all, good materials.

Button Sound Test

Disassembly

Disassembling the X15 is somewhat difficult. First, all skates and the screws beneath them ought to be removed, along with a single screw located beneath the sticker, roughly below the F of the FCC logo. Top and bottom shell can be separated now, though one has to take care not to rip the ribbon cables.

First, we have the large and very thick main PCB. Aside from the sensor and several connectors, not much can be seen on its top, but on the back, the MCU is located: An NXP LPC5516, whose datasheet can be found here. The main buttons sit on their own PCB, which connects to the main PCB through a ribbon cable and is fixated with four screws. The scroll wheel doesn't sit on that PCB, but is instead suspended in an encasing and directly routed to the main PCB with a 3-pin connector. The top buttons too have their own PCB, screwed into the top shell and connected to the side-button PCB with a 4-pin connector. The side-button PCB is then encapsulated in a plastic assembly and virtually inaccessible. A large ribbon cable connects it to the main PCB. Finally, a 2-pin connector connects the single shift-button switch to the main PCB. Four screws are used to affix the main PCB to the bottom shell.


As for the soldering and general quality of the PCBs, I'm unable to find any noteworthy flaws.