I just passed it a few minutes ago on the mobile version in first try (second try if you count a failed attempt I've had a few days ago). It wasn't as bad as I expected but I had some minor unfortunate events during some of the levels such as the ambulance nearly rolling, crashing a few times into some cars, one of trucks ran over a patient (thankfully didn't kill him but got him stuck under the truck for a few seconds) and almost made the time ran out and it happened at level 11 at last patient remaining which was really annoying but the patient got up in last couple of seconds.
The time limit is of course the main problem when you do it in Portland and sure it does get tight in some of the levels (thankfully I've had 24-25 seconds per patient in most of the levels, but even then there are times when you need to hurry up to pick up a certain patient or risk running out of time) and there are some times you will complete a level with only few seconds remaining on the clock (if you are lucky maybe 20-30 seconds remaining) but hopefully you will make it in the end. Of course it is luck based on how the patients spawn (hopefully not into stupid places like the basketball court and the alley behind the Ammunation, both of which happened on a previous failed attempt a few days ago) and the amount of time received per patient.
But yeah in my opinion you should try it in Portland as no gangs hate you (if you do it at very beginning of the game, like I did), patients spawn close to each other in most cases and the mission can be completed in about 40 minutes. Just take your time and you will eventually succeed in the end. Hope this helps!
Oh and here is the save game I just uploaded a few minutes ago, it's for Android version only but it will help people who can't pass this mission if they happen to also play on Android:
The only thing to note is that I have already done pretty much everything that could be done in Portland at beginning of the game and I hope this won't disappoint people who just want Paramedic mission done and nothing else. I've actually had done in 2015 a Paramedic mission completed only save for PC but that save is long gone and its link on SNP has also expired, so this is the only option for people who have the mobile version of GTA 3 and even then only for Android phones. Hope this helps!