The example can be found here https://forum.aspose.com/t/performance-issue-pdf-to-png/263995.
Which mechanism does the online pdf editor PDF Editor | Online and Free | Aspose.PDF use? It seems to be pretty fast.
We believe that an issue has already been logged for the situation discussed in the referenced thread. We will surely inform you once some progress is made regarding ticket resolution.
The online free Apps are combination of different Aspose APIs. Also, the server where they are hosted may offer enough memory for such features to execute fast. Nevertheless, your concerns have been recorded and we will surely inform you once we have some updates for you. We sincerely apologize for the inconvenience faced.