It is not compulsory or needed to read Qur'an on mobiles with wudu or purity of menses as scholars classify the Qur'an on mobiles (soft copies) to not be related to the rules that apply to the written Qur'an (hard copy).
They explain that the Qur'an on mobiles is just a wave pattern of electrical and magnetic energy vibrating through space and therefore ...
Ghusl (washing whole body) is obligatory not only after ejaculation but even without ejaculation if penis inserted in woman vagina once it becomes obligatory.
If case of shortage of water you can have Tayamum (dry ablution).
The hadith doesn't explicitly say that 1500 sahabi made the ablution, but it says that this amount was present when this happened. So we can't exclude that some of them have been in a pure state. Note that scholars such as ibn Hajar discussed the amount as the reports seem to have a certain difference.
The hadith can actually be explained by another version ...
Well, I don't think its logical to assume that between zuhur and Asr all of them had their wudu broken... usually you can pray zuhur and asr with same wudu; especially if you eat and drink less like they used to... wallahu aalam.