https://www.crutchfield.com/S-N7WPy0GNhJS/p_310YU4MB/Kanto-YU4-Matte-Black.html

Get those. Better speakers than your T15's, amplification is built in, and they have two sets of analog inputs (one each for your turntable + your cassette deck). They have optical digital inputs as well, should the need ever arise.

One of the analog inputs uses a 3.5mm jack, not RCA, so you will need to grab a dual RCA to 3.5mm TRS cable. Should only cost a few bucks.