Viewxls macro causes out of memory error and then fails to render

Creating on behalf of customer:

The problem occurs while rendering the content from the attached Excel Spreadsheet using the viewxls macro.
When the page the macro is used on is about to display the application is under high load, meaning both memory and cpu usage increase above normal, and one of the following things happens:

1. The page is displayed but the rendering of the macro fails with an OutOfMemoryError
2. The page is not displayed and the upstream Apache HTTP server replies with

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /confluence/display/prozesse/Kennzahlenprotokoll.

Reason: Error reading from remote server

Regardless of which of the both cases occurs, eventually the whole application becomes unavailable and has to be restarted. Also requesting other pages (without the macro) is not possible anymore.

It seems that the sheet "Leading Diagramm" is causing the problems (though other sheets do also cause high load).

When more memory is given to the Java process it requires more concurrent users to cause the aforementioned problems. But even with 1,5 GB of memory 4 users are enough to cause the problems.

Below you can find the Wiki markup of the page embedding the Excel content:

{toc}

h2. Leading Kennzahlen

{viewxls:page=Kennzahlen|name=4_Kennzahlenprotokoll_Atlassian.xls|sheet=Leading Diagramm|row=80|col=7}

h2. Lagging Kennzahlen

{viewxls:page=Kennzahlen|name=4_Kennzahlenprotokoll_Atlassian.xls|sheet=Lagging Diagramm|row=160|col=7}