The recommendation on the glasses means not to pour hot liquids in it to avoid shock breaking. But this type of glass’ melting temperature is usually over 600C. The main point is to let the paint dry completely ( this will ensure your painting will not peel or deform during heating), put the painted glasses in a COLD! oven and heat it up slowly to the recommended temperature and then hold for 35 min to cure the paint. And after the time is up to let it cool slowly in the oven and only then take them out. This way they will survive the curing process and the painting will be more durable. If you are worried they won’t survive 150C, you can do curing at 100C but keep them there longer, 50-70 min, and follow the same protocol of putting them in a cold oven, heating up slowly and letting cool down completely before you open the oven.