I wouldn’t automatically call the increase bad. If previous contributions were unrealistically low, the apartment may always have looked cheaper than it truly was. Higher reserves could make the building more resilient. My caveat is that paying more does not by itself prove the reserve is...
Plumbing access could be the biggest sequencing trap. Establish where existing water and waste lines run, whether drains can be inspected, and whether new bathrooms require opening the slab. Quotes should separate service installation from excavation and reinstatement. That makes it easier to...