Remember that it doesn't cost anything to Waitlist and that they remain current for three days during which time they (hopefully) consider filling them.
SQ certainly do release more seats as they review the loads during the year. To me, with SQ having just 1 J saver award available on each flight looks like they have a default setting this far out. When they actually start analysis of the loads this will change.
Depending upon your personal travel plans and comfort levels the 15% might be a worthwhile price to pay to lock the plans away and move on to other activities.
Of course, here at AFF, we encourage you to finesse the perfect booking at the optimum points price which will possibly be closer to departure maybe 5-8 months before.