At risk of being downvoted, I'll say "don't debug using a debugger".
Use solidity events, and log profusely in your contracts. Logging is dirt cheap when it comes to gas, and it's easy to capture every Solidity event using web3.js event listeners, which parse the output to the degree where you can log it straight to a JSON logfile with a couple of lines of code.
So log everything that happens in your contracts to a logfile, and you can reconstruct what happened. The bonus part of this is if you have some issue later in production, and you have all this gas-cheap logging enabled, you can likely find the source of your problem quickly, post-mortem. This technique has saved me numerous times in all my years of development. It's the "bigdata" approach (but at small scale)
I've debugged over 1000 lines of solidity this way already with complex business logic, it's worked pretty well. Event logging has been one of the more delightful features of Ethereum that I've discovered.
transactions are taking 15-30sec to process.
Use a testrpc implementation or hack up geth to mine every second like I did. That also helped me debug very quickly. See links below.
Some links for further reading:
web3.js listening for all events
Bunyan, a node.js logging module
Hacking Geth to make it mine once/second
ethereumjs-testrpc AFAICT is the most mature EVM emulator for testing.
If you do mostly on-blockchain interactions, then Dapple is a unit test framework for Solidity. I haven't used it but I hear it's good. (my app is mostly off-blockchain right now, so I haven't needed it).
And finally, a good way to stop making hard to find bugs is to write black box unit tests. I hacked up my own unit test framework, but I hear truffle is pretty mature now so that might be a good choice to start with.