According to NASA's eclipse page, there will be a total solar eclipse of the Sun on August 12, 2045. It will be total in Redding, CA at 16:17. To demonstrate the speed of Gravity Simulator, this simulation is started using JPL's solar system data for July, 2015. Depending on the speed of your computer, it should take about 5 seconds to propagate all the solar system's planets and Earth's moon from 2015 to 2045 and accurately reproduce this eclipse as viewed from Redding. Press "P" to begin the simulation.
 
http://orbitsimulator.com/gravitySimulatorCloud/simulations/1445485644214_Propog ate_to_2045.html

That's about the speed I get on my old Windows 7 computer.  It takes about 1 minute to run this sim.  But on my Windows 10 machine and a newer Mac, the sim runs in about 5 seconds.

My 12-year old Windows XP computer runs it slightly faster than my 6-year old Windows 7 laptop.  It just seems that computers have gotten a LOT faster over the last 2-3 years.  Even the latest smartphones and tablets run this sim in about 5 seconds.
 
Running the Windows version of Gravity Simulator, my new Windows 10 computer is about 4x faster than XP or 7.  But the browser version of Gravity Simulator runs about 25x faster on newer computers than on XP or 7.
 
Get a new computer, Frank!  You'll love it. They're just faster all around.
Windows 10 takes about 20 seconds to boot up.  Windows XP and 7 take several minutes.
 
The browser version looks horrible in IE.  IE does not support a lot of the javascript and HTML5 that more modern browsers such as Firefox and Safari do.  Windows 10 comes with Microsoft Edge, which is much more up to date than IE, and is comparable to Firefox and Safari when running all the latest javascript and HTML5 features.

As I was running some test to answer your questions, I noticed something I've never seen before.  The executable version runs MUCH faster if you open a file by clicking on a link from my web page, rather than by opening a file saved on your computer.
 
For example, click this link:  http://orbitsimulator.com/gravity/simulations/2045f.gsim
Notice the speed, then try saving it, and re-opening it from your computer.  On both my Windows XP and Windows 10 machines, the one opened from the web page works faster, and is comparable in speed to the html version of the program: http://orbitsimulator.com/gravitySimulatorCloud/simulations/1445717816562_speedT est.html
 

Quote from frankuitaalst on 10/24/15 at 14:48:47:

I guess I don't know what an "explorer" is.  I thought you meant browser.  Do you mean processor?  My Windows 10 has an  i5-4570 with 4 cores.
 
On my Windows XP computer, I get about 10 seconds, just like you, assuming I run it from the link.  If I save it and run it from my hard drive, it takes about 2 minutes.
 
On my Windows 10 computer, the executable from the link takes 2 seconds, and from a saved file takes about 20 seconds.  The HTML version takes about 3 seconds.  A Mac an iPad and a new smartphone also take about 3 seconds.

My older iPad had that performance.  But last month we were issued new iPads at work.  The new one is just as fast as my Windows 10 computer.
Here's a Youtube showing a speed comparison between the executable and the Windows 10.  This is before I discovered that my Windows 10 computer runs the simulation very slowly if I run it from my hard drive.  But it still shows you a speed of about 10 years / second for the HTML version.
https://www.youtube.com/watch?v=F9Dof7EzSvo