I scoped it out. 15 SR is chipsealed from Guelph Line to the 5th Line Nassagaweya (i.e. 2 roads east). It looks like they did a decent job this time - it is bedding down quickly, the car tracks are pretty solid but there is obviously still loose gravel between the car tracks.
5th Line Nassagaweya is only a through road to the north and it has not been chipsealed, nor has any of the 20th Sideroad east of Guelph Line. So you can detour via 5th Line north to 20th Sideroad. Or you can just ride in the car tracks and beware that you have little room to maneuver side to side (i.e. slow down). It appears that they are going to be doing the 4th Line also, but there's no sign of either the 5th Line or 20th SR being done, nor do they appear to need it.
For those who haven't done 20th SR before ... there are certain places on that road that always have sand, particularly near the east end where it ends at the town line. The town line is rough in both directions and the 22 SR east of the town line is especially bad (last winter did a lot of damage).
15 SR has sand westbound in the first set of bends east of 25 because of gravel that has been sloppily applied in the shoulder and it's spilling over onto the pavement, and that's an uphill right and you can't see it until you are almost on top of it ... careful.
As for proper pavement versus chipseal ... I grew up in this area. Be glad there is anything beyond just a gravel road! Most of those were all gravel back then. The town line at the east end of 20 SR was gravel, except between 17 and 20 SR, until only a couple of years ago. It's rough because they just chipsealed right on top of the old gravel road bed without doing anything to fix the road bed itself. At least you can ride on it with street tires now. Proper paving - like they did on 20 SR west of Guelph Line a couple years ago - requires reconstructing the road bed and that is really expensive. A layer of chipseal now and again (every 4 - 6 years, it seems) is cheap. Only the major high-traffic roads in that area use proper pavement, ALL the rest of them are chipseal. Beats gravel ... so you can't ride on it for a week or two after they re-apply the chipseal ... Big deal.
I doubt if the local residents like the rocks, dust, and cracked windshields during that time when the chipseal is bedding down ... Might not be many bikes going past in that time but it's a mess if you live on that road during and right after the chipseal job. But again, it beats having just a gravel road, and it's cheaper than proper pavement.
At least they put down a layer of pavement before the chipseal, to hopefully even out the bumps. The last section of 15 SR west of 25 is bumpy because they didn't do that the last time ... they just chipsealed on top of the broken pavement ... now it's still broken pavement with chipseal on top of it.
It will all be OK, it just needs a little time. I'll run through in my car driving on top of the loose stuff (out of the normal car tire tracks) to help it either bed down or scatter ...