Like the guys have said, DOMS is not necessary for you to have had an effective workout. Like wwewrestlingguy I tend to get a little sore at the start of the 15s if I have done a 2 week SD. If I SD for one week only then the soreness is reduced. During 10s and 5s I seem to have a little soreness all the time.
For most exercises, if your calculated starting weight for 15s is less than around 50% of your 5RM you may want to change your increments.
eg. If for an exercise your 5RM was 200lb and your 15RM was 130lb you might have planned out your 15s with 80, 90, 100, 110, 120, 130. However, I reckon it would be better to start with 100 and work up to 130 somehow. Perhaps 100, 110, 110, 120, 120, 130 or 100, 100, 115, 115, 130, 130 or some other route?
If you have started with less than 50% of your 5RM you can always do more reps if it feels really light. I tend to do around 20-25 reps the first week of 15s just to really get a burn, but I am only doing one set of each exercise and I always start with a weight that is around 50% of my 5RM weight.
Be careful how you apply this though as if you tried to do this for dips you would need to include your body weight in the calc. So if you weighed 200lb and your 5RM was with 100lb added weight you might not need to add weight at the start of 15s (50% of 300lb = 150lb, still 50lb less than bodyweight. Using bodyweight at start of 15s would be about 200/300 = 66% of 5RM).
Re forearms: If you avoid using straps for chins, bent over rows, SLDLs and shrugs you will not need to do any direct forearm work. If you find that this compromises your heavier sets then just use straps sparringly until your forearms have caught up. I still have to use straps for shrugs as by then my forearms are shot!
