utg is unknown, utg+1 is a 9/7/3 over 1.7k hands, folds to cbet 42% of the time

should i be raising pf more? cbetting more? etc

PokerStars No-Limit Hold'em, $1.00 BB (9 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

SB ($102.15)
BB ($98.50)
UTG ($47.70)
UTG+1 ($100)
MP1 ($50)
MP2 ($159.05)
MP3 ($102.50)
Hero (CO) ($100)
Button ($111.65)

Preflop: Hero is CO with A, K
UTG bets $3, UTG+1 calls $3, 3 folds, Hero raises to $11, 4 folds, UTG+1 calls $8

Flop: ($26.50) 5, 6, A (2 players)
UTG+1 checks, Hero bets $15, UTG+1 raises to $35, Hero?