My responses to these two posts might help:
Essentially,「です」and「います」are usually not spoken in full, and are pronounced as "des" and "imas" respectively. However, sometimes it is spoken in full, as "de-su" and "ima-su", to add an emphasis.
Generally, the "u" sound, when paired with a consonant, like "su" or "ku", becomes almost silent and turns into a "s" or "k" sound respectively.
There is no rule against fully pronouncing the the "u" sound, but since Japanese people usually speak quite quickly, the "u" sound usually ends up almost silent. However, as Tony-S10さん said, it is likely that the person reading the script is emphasising the "u" sound to emphasise the spelling of the word.
I hope that helps イリニさん, and thanks for your help everyone!