The ACL report definitely worth a look, although I'm afraid it's disappointing reading in some ways.
ATMs Start of s15 vs start s14 -1%
ATMs Start of s15 vs end s14 -0.4%
ATM Seats Start of s15 vs start s14 +0.4%
ATM Seats Start of s15 vs end s14 +1.3%
Given the increases/cancellations listed by airline later in the report, it is perhaps surprising that the net increase in seats is so low. However, one of the graphs of movements by week suggests that May is quieter than last year i.e some flights start later in the season than s2014. In this context also, Vueling & Iberia Express only begin their new services part way through the summer, Ryanair's 8th based a/c is only in August and Easyjets 9th from June. Virgin's extra capacity to MCO & LAS is only peak season. It could mean therefore that the season gets off to a sluggish start but improves later.