Luton zone transits are nothing too much to worry about. As noted already, the E-E lane depicted on the map is not very strongly enforced, and a N-S transit via the threshold is often granted. As for not above 1500ft, I have transited at 1900-2200 before, since as long as you are going North-south and over the landing threshold, the controllers seem happy about the safety margins with heavy traffic conflict. I have also received transit clearance via the M1 west side from Hemel to Cranfield, so just call up on the day, ask for a zone transit and see what you get.