Ergo uses the linear least square method to calculate difficulty. This function is based on the past eight epochs (8x1024 blocks), as described in this paper to obtain a target block interval of 120s (2 minutes), on average, during steady-hash.
Autolykos will adjust slowly in response to fluctuating hashrate, but this helps prevent adversarial hopping. This algorithm has a 1.9% error rate compared to bitcoins 9.1% error rate (exponential 10% hash rate growth).
You can use the difficulty & epoch monitor to get an estimate for the next difficulty due.
Why 2 minutes?
As Ergo is a P2P cryptocurrency that supports smart contracts, there is need for security buffer for all the issues and attacks possible; propagation delays, spam attacks, verifier dilemma etc
Can it be quicker?
Ergo already uses an epoch length of ~1.5 days (with normal block rate), compared to Bitcoin's two weeks. Having a quicker difficulty readjustment can lead to Timewarp attacks. More epochs were considered, but the retargeting function is also non-linear, so it can adjust sooner than the linear function in certain popular scenarios; and it is unclear whether any hard-fork would be required at this stage.
There is a discussion ongoing on ergoforum regarding a potential improvement to this algorithm.