Are you feeding LO for 15 minutes on both sides usually, then pumping, or is this just what you're doing to relieve the clogged ducts?
If you're doing it normally, you're telling your boobs to make more milk so you will keep getting engorged and keep getting clogged ducts. Are you sure they are actually clogged ducts? If you hand express and watch your nipple, can you see bits where milk isn't coming out that it does later? You might just be feeling the relief of the engorgement or possibly you're feeling a let down (you can have more than one per feeding session). I wouldn't have thought you'd get a clogged duct so quickly after feeding or expressing, I would have thought it would take a while for the duct to get blocked up again. You might, however, be feeling your boobs start to fill up again if you've been telling them they need to make loads of milk quickly.
In an ideal world, you wouldn't express at all because the more you do, the more milk you'll make so the more engorged you'll feel and the greater than chance of problems. However, if you've been expressing a lot (and it sounds like you have!), you will probably need to reduce it slowly. Remember that every time you express until 'empty' your boob will think, "OMG, I'm empty, the baby is STARVING, quick, make more!". You have to leave a little milk in there to let your boob know it made too much. So I would slowly decrease the time you're spending pumping - you need to get it so that you're only expressing to relieve pain (and then nothing at all, unless you want to store milk), NOT so that you feel empty. You also don't need to time LO's feeding sessions and you shouldn't be doing a set number per side. Feed LO from one side until LO is done, then switch to the other side if LO is still hungry. Go to the other breast at the next feed.
