I know you mentioned that your computer doesn't do well with DS emulation, and I completely understand why that would make you think PS2 emulation is definitely out, but I would actually encourage you to give it a shot. DQ5 for PS2 is incredibly light on PC resources, and will often play at full speed (or nearly) on crappy computers, where a more resource-intensive game (like DQ8) would definitely be out of the question.
I think it has a decent chance of working well for you. If you need help with emulator configuration, there are plenty here that would be willing to help (including myself). It may not be viable, like you suspect, but I know from my experience that it runs way better than expected on crappy PCs.