Feasibility of very high temperature ac-dc switching power supply
Probably not a severe requirement- 105°C is not that hot, you can even get electrolytics easily that are rated for 125°C. Assuming (from your tag only) that the input will be AC you may require a fairly large electrolytic filter cap. At a sufficiently high switching frequency you may be able to use MLCC capacitors elsewhere in the circuit. 

The size might be an issue- usually high efficiency (which you want at high temperatures) can require a bit more size, and 15mm height (inclusive of housing?) is a pretty tight restriction. 

Expect more limited lifetime if it has to operate for a substantial duty cycle at very high temperatures and electrolytics are necessary. Temperature rating for e-caps is for a life measured in thousands of hours, not tens of years, so we usually like to operate at an average temperature much less than the rated temperature.