You would have to do a load calculation to know for sure, but ya, you have 150As. Lots of multi unit buildings have main breakers that are less then the sum of the individual unit disconnects. The sizing of the main is based on a load calculation (found in the NEC) which adds up the expected use of each unit and comes up with an expected load. The load calculations are based on the assumption that not all the units are going to draw max power at the same time. Sometimes one tenant will be drawing alot and sometimes another and rarely both at the same time.
Master Electrician, Air Conditioning & Heating Repair Company Owner. www.TECertifiedElectricians.com