Well....kind of.
I'm a ridiculously patient person, so waiting behind a column for 2 hours and watching patrols doesn't bother me.
So to specify, if you're crazy to wait obscene amounts of time to get through gunfights, wait for the AI to screw up, restart often and don't mind finding unorthadox methods and in some cases glitches to taking out a few enemies you're fine.
On the other hand if you're normal then no, pure stealth is impossible.
So far I'm focusing on H2H, tech aptitude, and stealth, I also pump a few odd points into pistols.
So for me a traditional level that lasts 45 minutes would last me about 1 hour and 30 minutes or more.
Also I never really bothered stealthing bosses, Just pumped them full of lead. So can't say much about that. Might try to play around with the bosses on a second playthrough. Also the noise generator is your absolute best friend.
And just to specify, there are enough stealth parts in the game to satisfy most stealth gamers but to "ghost" would be damn-near impossible.