Because it is mentioned in the very first post, I suggest to add Georg Klingenberg's report to the table:
Reported | OS | Version | GTK | slower -- | -- | -- | -- | -- [msg02989](https://www.mail-archive.com/users@lists.geany.org/msg02989.html) | Windows| 1.36 | ??? | no [msg02989](https://www.mail-archive.com/users@lists.geany.org/msg02989.html) | Windows| 1.37 | ??? | yes untimed
In his [reply](https://www.mail-archive.com/users@lists.geany.org/msg02992.html) he described the familiar behaviour: not the startup per se is slow, but the load time of each file (loaded at startup or later).