Ady1397, congrats on your new tank - it's only three times the size of mine.
When I was shopping for my 58
gal, I was concerned about the weight since I live on the second floor. After alot of research, I concluded that anything 90
gal or smaller would be OK so long as it was positioned as close to a weight-bearing wall as possible. I have my 58
gal in my livingroom with a 10
gal Q-tank beneath it. I am considering getting a 75
gal for the bedroom.
A catastrophic structural collapse is incredibly unlikely - especially in a building as old as yours with concrete floors. My building, in Queens, NY was built in the 20's and tit was built to last. Two inch dimensional lumber was not commonplace back then - they used timbers - big hunks of wood 4 - 6 inches thick and 8 inches wide!
A 155
gal is a HUMONGOUS tank, tho, and I would be more concerned about the repercussions should the tank itself suffer a catastrophic failure (a much more likely scenario than your floor collapsing).
I urge you to carefully check your lease and make sure there is no clause prohibiting aquaria.
Then, purchase a renter's insurance policy to protect yourself from damages should the tank ever leak or fail. $30,000 of coverage costs only $120 a year and it also covers you against theft and fire. Just make sure that the policy covers water damage (most do).