Meh, Sounds about right... Sounds like a rather friendly increase as well. Have you seen some the "penalty" interest rates? 33% etc??? So yeah, typical stuff. Frustrating, do what I did recently with a Visa. Just call em' up, and talk to a manager. Not some half sentient mouthbreather answering the phone but a manager, and just explain that you feel their increase is unwarranted given your years of trouble free card usage and that if they insist on increasing your limit that you will in fact pay the total amount due now and close your account.
They don't WANT you to pay off your cards, that's a death sentence to them. Worked like a charm, once way back, DISCOVER (remember them, the ANYONE can have a $7500 limit card company) did the same thing to me. After 11 years of flawless history Doscover got shuffled in a move and we straight up missed a payment. BOOM 23%!!!! Yeah They got paid off that month after refusing to fix it...
Discover has to be about the worst though, the most predatory anyway. Hunting down the shakey or recently established and giving them available balances way beyond typical.
I've had nothing but good luck though with American Express, not their Credit cards, cause they are just like any other card, but they Charge Cards are the Bomb. Handle your business, pay everything off at the end of the month. Win-Win and six years 433,000 points later trouble and drama free...