Merion has got to be my favorite course on WGT, and although if i hadn't missed an easy 5 foot birdie on 17 for a 53, It very hard to get a consistent round, there's always one or 2 spots which can de-rail your round in an instant. But what I do like are the weeds! Thats exactly how it should be 50/60% brush which will penalize you for any mistake or being too greedy so a birdie turns into bogey or worse!
As for #13, although Its says 134 yards, the hole is either on a downslope or the true yardage is well under the 134 yards. if i have side wind, i can take this much off 135 iron full spin {...} and still land within a yard. I've even over shot the green with 135 iron in 17 mph HEADWIND! so best to shave a few yards off the 134. If i have tailwind i will either use 120 PW with topspin, or take a lot off the 135 iron full spin. With headwind i will use 135 iron with a touch above full spin but a touch under 3/4 spin and always get it bang on. But as for 15, i could play a shot now and land within a yard, but same shot next time will land short! there seems to be no middle ground.
If you want a challenge then try Merion in uneven lies! Those easy birdie holes like #7 become a struggle and you're more likely to par than birdie (same with 4) Was a major fight just to score 59! But I love Merion none of those billiard table bethpage style greens here