You may not be able to have 1.5mm thick PBT keycaps on a Topre keyboard. The stock ones are fairly thin compared to some aftermarket ones because the slider housings interfere with the insides of the keycaps. On my RGB, I've tried quite a few keycaps that either make clicking or tapping noises as they come down, or stick, because they're too thick. I had to grind down the insides of some SA ones to get them to fit. You'll have the same issue on a regular Topre board because the slider housings are the same size. That being said, the keycaps that KBDFans sells are pretty nice, and seem thick enough. I've had their 9009, 2020, and BIIP sets, and liked them all. The 9009 had one of the Windows keys slightly rotated, but that seemed to improve on the other two. Currently KBDFans has the 2020 set back in stock, and a new black on dark grey BIIP set that looks like the stock black Realforce keycaps.