Since I'm on the second set of weather stripping in 5 years and you haven't changed the seals in 15 years I'd say you are over due.  Look for compression of the seal when the hatch is open or pinching, twisting, etc. . Won't take too long to replace. Make sure your cover doesn't slide around. 

If this was your first capsize in 15 years I'd say you are over due for some assisted rescue training and exercising. 

Yes there are hatch covers that are more "air tight". But be aware that my wife  is on the second set of those rubber hatches in seven years of use. Those hatch covers run about $80 each. Two or three per kayak.  Frames excluded.  . 

one of the major changes on hatches that was made on the chesapeake line was a hatch rim that got glued to the deck of the boat that provided a raised element around the hatch opening that was very effective in engaging with the gasket material. 

i don't know exactly when the change was made....but it is quite possible based on the age that you don't have these hatch rims on your boat.

prior to this change, in the old boats, this rim was not there and the gasket  just rested on the deck and it was very easy to leak.  installing the rim is easy and if you don't have the parts CLC could send you a set, for i am betting, a very reasonable price.   

between the hatch rim, fresh gasket material,and making sure you cinch down the straps tight, these should be very water-tight hatches.

h 

   Probably obvious but test at your house with a garden hose as you make modifications. 

   Appreciate all the helpful information in replies.  

@Grumpy - I'm not quite sure how this being my first capsize in 15 years means I am "over due for some assisted rescue training and exercising".  There is no direct correlation that I see.

   Assisted Rescue training......is just a catch all term for capsize and recovery training in deep water.  Which to be any good needs to practised at least once a year.  Which means you would have capsized , several times, at least once a each of those 15 years. This needs to be with assistance, another paddler/boat, and also solo. 

 Seems like every year my ability to heel hook back into the cockpit is a little less.  Might be a paddler weight problem. ;-)  Here is a link to a Gordon Brown You Tube video on the Heel Hook and assisted rescues.  

https://video.search.yahoo.com/search/video?fr=mcafee&p=gordon+brown+kayak+heel+hook#id=1&vid=4d3b4d67e89f1ef72005c94c92448aee&action=click

Most of........all of my .......unscheduled capsizes have been in still water waiting for other paddlers. Don't be put off by the rough water examples. 

   MtnMan,

Wondering if you resolved your leaking hatches issue? I just aquired a C17 and the hatches leak (and there is no rim around the hatch opening), and have been searching for a fix. The foam on mine is old, and have some replacement foam ready to install...