There will be grousing, but a business is a business, and when that business’s product is in high demand, the price moves. C’est la capitalism.
The Chicago Cubs broke out in a big way in 2015, and attendance came along with it. Demand for tickets was up, and the Cubs will increase prices for 2016 commensurate with that demand. Season ticket holders will soon receive their invoices for 2016 tickets, and that’s where the increase will first be seen. Single game tickets won’t go on sale until next year, but you can expect to see a similar increase there.
You can read about the increases here from Carrie Muskat and here from Danny Ecker, but the extremely short version is that tickets are going up across the board, with an average increase of 10%. Ticket prices had been largely flat since 2012 (for perhaps obvious reasons), so this is a significant, even if not unexpected, jump.