The game was much more enjoyable in the earlier stages than it has become. After Kenny the more enjoyable Really Big Upgrades are much more spread out (and smaller, perhaps). Also there's less to upgrade since most artifacts and such have been maxed. I can see that later there are things available, but not so much in the middle. Adding another artifact to unlock and increase or adjusting the upgrades that increase all gold production would help this lagging time.
Love this game.
Regarding the "slow" comments- the one or two times it slowed down for me when I finished that adventure I'd close out of my browser and reopen and it worked fine.
TIPS:
Dreams are super helpful. XP, Gold, and an extra move are wonderful.
When you have two lines, remember not only color but attack order- if you can clear the first line with your thief, then you might not want to put much onto the warrior, but focus on the ranger or wizard, etc.
 "Midas' Gold Plus"){kind=icon}
 "Dangerous adventure"){kind=icon}