Yes, you'll overtrain doing LT intervals and you also won't improve as quickly as possible either because that's not an optimum training programme. I'd do the following:
1. sprints, shortest ride of the week, 15-miles max. Do 5-8 all-out 100% sprints at to complete exhaustion with full-recovery in between.
2. LT-intervals, maybe do pyramid sets 1-2-3-2-1, up & down a hill, etc.
3. tempo, 15-20 min continuous, 4x4, long hillclimbs, etc.
One or two days of strength-training in the gym would help too if you can get it in.Hard to do real endurance workouts in the winter, 3-4 hours. It's easily to pile on the flab, so be careful with the holiday feasting.