Yeah, it is a 15 amp. So is it best to remove, take it to the hardware store to match up? That may be a lot of down time without power to the tank.
My GF has been pretty good with the tank. I'm getting away with a 90 gal in a studio.
Im an electrician and most home wiring is done with 12 awg... Its been code for a very long time... New homes and a good planner would use 10 awg for future loads... I wouldnt be able to tell you which way to go or what wire you have in your home so you should have someone look at it...
If you check the awg of the wire in all the outlets on that circuit and confirm they are all 12awg you increase the odds that there won't be a problem. What type of walls do you have in the apartment? Do you know if its sheet rock only or is it plaster and lathe? If you're planning on staying in this apartment for a while it might be worth having it done.
I would try 2 heavy duty 4's rather than the dc8.. Depending on you box it could be easier than you think to run another line..