Every 15 minutes except at 3AM?
Stackoverflow responses say it can't be done in one line.
I can't think of a way to get it in one line. Probably easiest is to split into two jobs.
*/15 1,2,4-23 * * * - this runs every 15 mins except between 3am and 4am
15,30,45 3 * * * - this should cover the delta