A project's progress which is executed with a globally spread virtual team has been found to be too slow. What can immediately speed up the project?

Get the team to a single suitable place

According to the hypothesis of the question. It depends on the type of project for example  if it is possible to assign some  of  the project to the finishing point by a third party with faster Possibilities or add some Machines to speed up production and increase accuracy or increase the number of staff and work extra shifts .

Of course in the framework of the project budget.  In the worst case, to avoid loss 

Every location there should be a person require in the position of "Project Co-coordinator". First he must be trained properly by the global project team before initiating the project.  It make more sense and will helps the virtual team to complete their project implementation globally  much faster than the other method of implementations.

For a project to be completed on time the most important thing never forget your time lines & keep proper eye on it and speed up where its neccessary.