transfer new fish from tank to tank?

Hello, in the past month i obtained a 15g aquarium and i thought hey might as well get some fish.  I went to the store and got 2 2.5in oscars, a 2in pleco, and 1 1.5"lionhead. That being said i didn't know anything about fish at the time, and afterwards in heinsites regret i studied up, which i should have done before.  So i decided after learning fish to tank water value and what will be needed, i decided to upsize to a larger tank (90gal.).  Im installing the tank tomarrow, and im going to let the tank settle for a day.*  I need to know if i can transfer my fish to the new tank as soon as possible without causing there stress levels to raise drasticaly?*  Notably one of the oscars is 2 days new (one died v.v and the store gave me a new one <3) and the other fish have been in there for about 2 weeks.
date notes : aquarium obtained nov. 2cd,  fish added the 10th, second fish added 22cd, new tank will be ready by the 26th
* = actual question to be answered