vorpX adds async timewarp to your Vive. The 45fps are not 45fps in your headset, you do not have to worry about this.
If you want, you can disable this behavior by disabling the FluidSync option (display page of the ingame menu). That is only recommended for games that can run at high frame rates though. Otherwise it’s A LOT better to leave this on for Vive.
If any Rift users are reading this: please also leave this option at the default value. For Rift the better value is Off (the default there) as the Rift does its own async timewarp.