The 155 and 170 have different engines.
155 has the Rotax 1503 non-supercharged aka NA - Naturally aspirated. The 155 hp engine was discontinued for 2020.
170 has the Rotax 1630 ACE NA (230 model has same engine with supercharger).
The Rotax 1630 ACE is the main engine for most of the newer SeaDoo models and was introduced in 2016.
Rotax engines | Sea-Doo Watercraft | Sea-Doo US
According to this site, the 1630 is loosely based on the previous Rotax 1503.
They control the hp output via computer tuning and addition of a supercharger.
I haven't heard of any problems with that engine.
The 1503 NA is a solid, proven engine and had been in production since the early 2000's.
I have put over 400 hours on the Rotax 1503 on a 2008 GTI 130, 2011 GTI 130 and 2012 GTI 155. The only problem I had was a failed head gasket around 250 hours. Fixed it and put on another 100 hours. Just sold that machine to upgrade, but it was running perfect and I'm sure it could go another 300 hours or more.
The only real DIY maintenance for the NA is oil and spark plug changes, which is very easy to do.
Expect to rebuild the pump every 100-200 hours.