Not sure if I completly understand your question, but I'll try to answer you best I can.
If your question is can you install TMO using patch 1.5, yes you can, but make sure you download the 1.5 version of TMO. Ducimus still offers a 1.4 version, but no longer supports it. So, DO NOT use TMO 1.4 on top of the U-Boat 1.5 patch. I also am not interested in the German boats, but the version also enhances the U.S. Fleetboats, so you made the right decision there. Go here to read about the TMO versions
http://www.subsim.com/radioroom/showthread.php?t=132330