systemd unit starts before boot delay timer

I have a service that I wrote myself. It consumes a fair amount of CPU, so I want to delay startup 15 minutes after boot in case I am doing something else with the system in the meantime. After that I want it to run like most services with Restart=on-failure.

I set up a systemd timer which seems to work fine, but then I don’t know how to configure the service. Everything I read says you must disable the service so to keep it from starting on boot, but when I disable it, then the symlinks in /etc/systemd/system are totally removed so the timer can’t find the unit to start it up. If I enable the service, it creates the necessary symlinks but then it starts right away on boot without the timer.

How to I properly install/enable/[insert correct verb here] the service while forcing it not to start before its timer fires?

This is running under Ubuntu 18.